1. Field of the Invention
The present invention relates to an optical semiconductor device, and particularly a light emitting diode (LED) device, having an optical semiconductor element encapsulated within a cured product of a silicone resin. Specifically, the invention relates to an optical semiconductor device which, as a result of incorporating a predetermined amount of (ΦSiO3/2) units (wherein Φ represents a phenyl group) within the encapsulating silicone resin cured product, suffers no discoloration at the lead surface, and exhibits excellent thermal shock resistance.
2. Description of the Prior Art
Optical semiconductor devices comprise an optical semiconductor element that is mounted on a lead formed of silver or a silver-containing alloy, or formed of a base material of iron, copper or the like and a silver plating layer covering the base material, with an adhesive such as a die bonding agent disposed therebetween. A silicone resin composition, and particularly an addition-curable silicone rubber composition, which is capable of forming a cured product that exhibits excellent rubber-like properties such as weather resistance, heat resistance, hardness and elongation, is typically used as a coating material or encapsulating material for protecting the optical semiconductor element from the external environment (see Patent Documents 1 and 2). However, in recent years, discoloration of the lead caused by corrosive gases within the environment penetrating through the encapsulating material has become a significant problem.
Silicone resins generally exhibit a high level of gas permeability. Accordingly, potential methods of addressing the discoloration problem described above include replacing the silicone resin with an epoxy resin having a lower level of gas permeability, or using a harder silicone resin. However, the cured products of these types of resins are hard and prone to cracking, and suffer from a concomitant loss in thermal shock resistance.    [Patent Document 1] US 2004/0214966 A1    [Patent Document 2] JP 2005-76003 A